Modern zoom lens systems differ from traditional zoom lens systems in that changes in the imaging system are not achieved through motion of optical elements along an optical axis. Rather, the optical properties of particular optical elements in modern zoom systems change through application of voltage, pressure, translation or rotations in planes that are not parallel to the optical axis. One example of the use of variable optical elements in a modern zoom lens system is replacing one lens in the traditional zoom lens system with a variable optical lens at the same physical location.
However, modern zoom lens systems that vary through changes in optical properties of one or more optical elements may introduce aberrations that act to limit imaging performance. These aberrations may worsen as the number of optical elements in the imaging system decreases. Aberrations that may limit the performance of these modern zoom systems include, for example, image curvature, chromatic aberration, spherical aberration, astigmatism, coma, and fabrication, assembly and temperature related aberrations.
Turning now to the drawings, wherein like components are indicated by like reference numbers throughout the various figures, FIGS. 1 and 2 illustrate an example of a prior art, four group traditional zoom lens system. In this traditional zoom lens system, movement of optical elements is generally parallel to an optical axis of the system. In a configuration 10 of the traditional zoom lens system as shown in FIG. 1, a combination of first through fourth optical elements 12, 14, 16 and 18 having focal lengths f1, f2, f3 and f4, respectively, is configured to form a sharp image at an image plane 20. A dashed line indicates an optical axis 21 of configuration 10. A marginal ray 22 entering configuration 10 of the traditional zoom lens system is focused at the intersection of image plane 20 and optical axis 21.
Continuing to refer to FIG. 1, first and second optical elements 12 and 14 may generally be considered as controlling the magnification of the traditional zoom lens system in configuration 10, while third and fourth optical elements 16 and 18 may generally be considered as controlling the location of image plane 20. Optical element 14 may be referred to as a “variator lens” or a “variator,” defined as an optical subsystem that controls magnification. Optical element 16 may be called a “compensator,” defined as an optical subsystem that controls focus. In some cases, particularly in zoom lens systems formed of a small number of optical elements, a given subsystem may simultaneously act as a variator and a compensator.
In FIG. 2, in an alternative configuration 10′ of the traditional zoom lens system, second optical element 14′ (e.g., the variator) is moved away from first optical element 12 along optical axis 21 and towards image plane 20, as indicated by an arrow 24, so as to effect a magnification change. In order to keep image plane 20 at a fixed location relative to fourth optical element 18, third optical element 16′ (e.g., the compensator) is also moved towards image plane 20 along optical axis 21, as indicated by an arrow 26. Through a combination of both of these motions, magnification of alternative configuration 10′ of the traditional zoom lens system is altered from that of configuration 10 shown in FIG. 1, while the image plane location remains fixed. In other words, a marginal ray 28, which enters closer to the edge of first optical element 12 than marginal ray 22 of FIG. 1, may now focus at the intersection of image plane 20 with optical axis 21.
As illustrated in FIGS. 1 and 2, the movement of the variator and the compensator in prior art, traditional zoom lens systems requires space along the optical axis. That is, no other optical element may be located within a space through which second optical element 14 must move to form configuration 10′, for example. A similar requirement for space is common to traditional zoom lens systems that require movement of optical elements along the optical axis; consequently, it may be difficult to reduce length of traditional zoom lens systems along the optical axis.
Modern zoom lens systems may reduce or eliminate the need for physical movement of optical elements along the optical axis, thus reducing overall length of the system as compared to traditional zoom lens systems. However, limitations of these modern zoom lens systems inhibit further improvements in imaging quality, size and cost. For example, currently available modern zoom lens systems require at least two actuated or variable elements to vary magnification and focus simultaneously. Also, certain modern zoom lens systems require an actuated system to control focus, which requires a certain number of elements to vary in order to keep the image in focus.